1. Field of the Invention
The present invention relates to a diagnostic ultrasound apparatus, and more particularly to a diagnostic ultrasound apparatus which can display changes of ultrasound image data with the lapse of time along a desired sampling line in a two-dimensional ultrasound image.
2. Description of the Prior Art
Generally, in the M-mode display of ultrasound diagnostic apparatuses, biological data (indicated by brightness and the like) of a living body taken along a specified ultrasound beam line (hereinafter referred to as the "M-mode scanning line") is plotted on the Y-axis and time is indicated by the X-axis, and this makes it possible to display biological changes, namely the state of motion, in the living body with the lapse of time on the M-mode scanning line.
In the prior art diagnostic ultrasound apparatus, the M-mode scanning line is obtained as shown in FIG. 1. Namely, an ultrasound probe 10 (hereinafter referred to as the "probe") carries out a B-mode scanning with respect to a diagnosed region in a patient such as a heart 22 thereof. The B-mode scanning includes a plurality of ultrasound beams 32 which are emitted from the probe 10 so as to form a sector shaped scanning area, for instance. On the basis of the echo data obtained by the B-mode scanning, a two-dimensional ultrasound scanning image, that is a B-mode image 20 as shown in FIG. 1 can be obtained. In this state, one ultrasound beam line 34 within the ultrasound beam lines which form the B-mode image is designated as an M-mode scanning line (sampling line). The state of motion of the heart with the lapse of time along the thus-obtained M-mode scanning line is indicated as the M-mode image on a display monitor of the diagnostic ultrasound apparatus.
Hereinafter, detailed descriptions are made with reference to the case where a mitral valve of a heart of a patient is observed by the M-mode scanning using the conventional diagnostic ultrasound apparatus. First, an operator confirms whether or not a mitral valve 28 of a heart 22 of the patient, which is to be observed, appears in the B-mode image 20 displayed on the monitor. Then, in the case where the mitral valve-28 is displayed, an M-mode scanning line 34 which passes through the mitral valve 28 is designated from ultrasound beam lines 32 which form the B-mode image 20.
Once an M-mode scanning line 34 is designated, transmission and reception of ultrasound waves are carried out only for this M-mode scanning line 34 by the probe 10, and biological data of the patient, that is the motion of the mitral valve 28 obtained along the M-mode scanning line 34 is displayed on the monitor. The changes in the patient along the M-mode scanning line 34 with the lapse of time becomes the M-mode image, and this M-mode image enables the operator to carry out observation/diagnosis of the state of motion of the mitral valve 28 of the heart 22 of the patient.
However, in such prior art M-mode displays, M-mode images can only be obtained along the M-mode scanning line 34 designated within the ultrasound beam lines which form a B-mode image. Moreover, in such an M-mode display, if the M-mode scanning line 34 is not substantially perpendicular to the portion being observed, that is in this example the mitral valve 28, it makes it impossible to obtain accurate observations of the state of motion of the mitral valve 28. As a result, the operator needs to estimate the position and motion of the mitral valve 28 and accordingly has to manually fix the position of the probe 10 itself in order to get the M-mode scanning line 34 to pass perpendicularly through the mitral valve 28. As a great deal of time is required in order to carry out such positioning of the probe 10, it is not possible to achieve the long-desired goal of shortening the time required for carrying out diagnosis.
Furthermore, since the object to be observed such as a heart is located within a body of a patient, it is surrounded by the rib bones of the patient. Therefore, when a diagnostic procedure is being carried out, for example when a diagnosis is being carried out on the cardiac function of a patient, the transmission and reception of ultrasound waves must be carried out through the space between the rib bones of the patient. This makes it very troublesome to arrange the probe 10 at an optimum position for viewing the specific portion of the heart to be observed such as a mitral valve. Accordingly, there is diminished reliability for such diagnosis.